In order to improve the erosion resistance of composites formed from certain polyimides such as PMR-15 resin, a spray coating procedure has been utilized using dilute solutions of a polyamic acid made from substantially equimolar quantities of pyromellitic dianhydride and 2,2-bis-[4-(4-aminophenoxy)phenyl]hexafluoropropane. While workable, this procedure is fraught with operational difficulties. In particular, numerous passes and thermal processing steps are required in the spraying operations in order to build up the coating to the desired thickness. Also, spraying of flammable chemical solutions requires the exercise of care from the safety standpoint, and can involve environmental considerations.